Back up here at 32,000 feet, I'm reviewing a slide deck sent to me. It is a Power Point 2007 deck saved in the PPTX (latest) format. It was built on a PC. I received it and attempt to open it with Power Point on the Mac. It opens yet barfs on a number of slides with a "I can't read this" error. I close it and open the file in Keynote. Opens fine. All slides can be read, no problem. From Keynote, I export a copy into Power Point. Power Point on the Mac now opens the exported version perfectly.